Re: [PATCH 2/2] memcg: do not report racy no-eligible OOM tasks

Michal Hocko
2019-01-08T11:46:42Z

On Tue 08-01-19 19:39:58, Tetsuo Handa wrote:
> On 2019/01/08 17:14, Michal Hocko wrote:
> >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> >>> index af7f18b32389..90eb2e2093e7 100644
> >>> --- a/mm/memcontrol.c
> >>> +++ b/mm/memcontrol.c
> >>> @@ -1387,10 +1387,22 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> >>> .gfp_mask = gfp_mask,
> >>> .order = order,
> >>> };
> >>> - bool ret;
> >>> + bool ret = true;
> >>>
> >>> mutex_lock(&oom_lock);
> >>
> >> And because of "[PATCH 1/2] mm, oom: marks all killed tasks as oom
> >> victims", mark_oom_victim() will be called on current thread even if
> >> we used mutex_lock_killable(&oom_lock) here, like you said
> >>
> >> mutex_lock_killable would take care of exiting task already. I would
> >> then still prefer to check for mark_oom_victim because that is not racy
> >> with the exit path clearing signals. I can update my patch to use
> >> _killable lock variant if we are really going with the memcg specific
> >> fix.
> >>
> >> . If current thread is not yet killed by the OOM killer but can terminate
> >> without invoking the OOM killer, using mutex_lock_killable(&oom_lock) here
> >> saves some processes. What is the race you are referring by "racy with the
> >> exit path clearing signals" ?
> >
> > This is unrelated to the patch.
>
> Ultimately related! This is the reasoning why your patch should be preferred
> over my patch.

No! I've said I do not mind using mutex_lock_killable on top of this
patch. I just want to have this fix minimal.

--
Michal Hocko
SUSE Labs